1. Field of the Invention
The present invention relates to a package for a semiconductor integrated circuit such as large scale integration (LSI), very large scale integration (VLSI), ultra large scale integration (ULSI) or gigascale integration (GSI), etc., a module in which the package is attached on a packaging substrate, a multi chip module (MCM) in which a plurality of semiconductor chips are mounted on the packaging substrate, and a method for manufacturing the module.
2. Description of the Related Art
FIG. 1 is a perspective view showing an example of a ball grid array (BGA) structure, partially cut away, of a semiconductor package being employed currently. In this BGA, a silicon chip 102 which has a thickness of 300 xcexcm to 450 xcexcm or more is mounted on a substrate 101 acting as xe2x80x9can interposerxe2x80x9d. Bonding pads disposed on perimeter of the silicon chip 102 are connected to another bonding pads disposed on a surface of the substrate 101 by bonding wires 103. Also, the bonding pads formed on the surface of the substrate 101 are connected electrically to solder balls 104 which are provided on a back surface side of the substrate 101, via through holes formed in the substrate 101. Then, a package is formed to have such a shape that the silicon chip 102 is covered with mold resin 105. Then, a module is constructed by connecting the silicon chip 102 to a packaging substrate via the solder balls 104. However, a thickness of the semiconductor package shown in FIG. 1 is considerably thick, such that the minimum thickness is about 1.2 mm. Therefore, the request for reducing the package thickness so as to reduce the geometrical size, weight, etc. of the mobile device, etc. in recent years has not been achieved.
Therefore, in order to greatly reduce the thickness of the semiconductor package, the respective thicknesses of constituent materials of the package were reduced. However, by simply reducing the thicknesses of constituent materials, the package warps further and product flatness cannot be assured. For example, in the case of the package of 0.12 mm thickness and a constituent material of molding resin, which has a Young""s modulus of about 12 to 25 Gpa, the package warps a large amount, such as about 1.5 mm relative to a length of 20 mm. In addition, because the rigidity of the constituent material per se is high, the resin cracks due to the small displacement, causing product reliability to deteriorate.
The present invention has been made to overcome the existing problems as described above. Then it is an object of the present invention to provide a flexible package with lower rigidity, and also to assure flatness of the flexible package, by reducing the warpage of the flexible package, as a single product.
It is another object of the present invention to provide a flexible module that can reduce its overall thickness and have high packaging reliability, the module employing the flexible package.
It is still another object of the present invention to provide a flexible module which can be attached on a curved surface such as the side wall of a pipe, a motor, a pen etc. and also can have the lower rigidity and the high packaging reliability.
It is a yet still another object of the present invention to provide a MCM which can be assembled by laminating a plurality of semiconductor chips along the thickness direction and also can have the small overall thickness and the high packaging reliability.
It is a further object of the present invention to provide a method for manufacturing the module, which can assemble above-mentioned package easily and simply on a packaging substrate.
In order to achieve the above objects, a first feature of the present invention inheres in a flexible package, which has a low rigidity substrate (referred to as a xe2x80x9cflexible substratexe2x80x9d hereinafter) and a low rigidity semiconductor chip (referred to as a xe2x80x9cflexible semiconductor chipxe2x80x9d hereinafter) mounted over the flexible substrate. On a principal surface of the flexible substrate, plurality of metal wirings are disposed. On a surface of flexible semiconductor chip, a plurality of bonding pads are disposed. The flexible package of the first feature further has joint metals for connecting electrically the plurality of bonding pads and the plurality of metal wirings respectively and a sealing member sandwiched between the flexible substrate and the flexible semiconductor chip.
According to the first feature of the present invention, the thickness of the semiconductor chip is reduced smaller than the normally-used thickness so as to reduce the rigidity of the chip. As the semiconductor chip, an element semiconductor such as silicon (Si), germanium (Ge), etc. or a compound semiconductor chip such as gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide (InP), silicon carbide (SiC), etc. may be employed. Further, the rigidity of the overall package can be reduced by reducing thicknesses of respective constituent parts of the package such as the flexible substrate, etc. Therefore, generation of the package crack due to displacement can be avoided. In addition, since the sealing member is sandwiched between the flexible substrate and the flexible semiconductor chip, the warpage of the package can be suppressed extremely small. Hence, flatness of the flexible package as a single product can be assured sufficiently. In particular, if the sealing member is composed of material having a low linear coefficient of thermal expansion (CTE), desired and normal flatness can be attained with the low rigidity structure. On the other hand, the flexible package can be attached onto the curved surface, employing the nature of the very low rigidity. And, such package is applicable to the IC card, etc. by utilizing the technical advantage that the package has a small thickness and has low rigidity.
A second feature of the present invention inheres in a flexible module having a packaging substrate, a flexible substrate disposed on the packaging substrate and a flexible semiconductor chip attached over the flexible substrate. On the principal surface of the packaging substrate, a plurality of packaging wirings are formed. The flexible substrate has a plurality of metal wirings connected electrically to the plurality of packaging wirings respectively, on a principal surface of the flexible substrate. The flexible module further has joint metals for connecting electrically the plurality of bonding pads and the plurality of metal wirings respectively. And a sealing member is sandwiched between the flexible substrate and the flexible semiconductor chip.
According to the second feature of the present invention, the flexible semiconductor chip which is formed thinner than the normally-used thickness so as to obtain the lower the rigidity. Further, since the thicknesses of respective constitute parts such as the flexible substrate, etc. are thinned, the rigidity of the overall module can be reduced. Therefore, even if stress is generated due to difference between the CTEs with the temperature history required for thermal process in the assembling stage, or due to the variation of the environment temperature in the usage stage, such stress can be relaxed. For example, since the linear CTEs of the packaging substrate and the semiconductor chip are largely different mutually, the packaging substrate is relatively expanded rather than the semiconductor chip at higher temperature. And, the packaging substrate is relatively contracted rather than the semiconductor chip at lower temperature. However, in the module according to the second feature of the present invention, since the thickness of the semiconductor chip is small, margin of the displacement in the vertical direction of the surface of the semiconductor chip is large. More particularly, since the semiconductor chip can displace freely in the vertical direction of the surface, the stress can be relaxed. Therefore, destruction of the inner structure caused by the temperature change is suppressed and thus the packaging reliability can be improved. As a result, the reliability as the product of the module can be assured. Also, since the sealing member is sandwiched between the flexible substrate and the flexible semiconductor chip, the warpage of the module can be reduced very small and thus the flatness as the single product can be maintained sufficiently.
Since the module according to the second feature of the present invention has the low rigidity structure, a mode in which the packaging substrate is so configured such that it has a curved surface can be achieved. Therefore, curved surface such as a pipe, etc. can be employed as an object to be attached. In addition, the module may be applied to the IC card, etc. by utilizing such merit that the module is formed thin and flexible.
A third feature of the present invention inheres in a MCM, which is at least constructed of a packaging substrate, first and second flexible packages. Each of the first and second flexible packages has a substantially same structure as already stated in the first feature of the present invention. On a principal surface of the packaging substrate, a plurality of packaging wirings are formed. The first flexible package has a first flexible substrate, a first flexible semiconductor chip attached over the principal surface of the first flexible substrate, and first joint metals connecting electrically the first flexible semiconductor chip and the first flexible substrate. The first flexible package further has a first sealing member sandwiched between the first flexible substrate and the first flexible semiconductor chip. On a principal surface of the first flexible substrate, a plurality of first metal wirings are disposed. And the first metal wirings are connected electrically to the plurality of packaging wirings respectively. The first flexible semiconductor chip has a plurality of first bonding pads on a surface of the first flexible semiconductor chip. The first joint metals connect electrically the plurality of first bonding pads and the plurality of first metal wirings respectively.
And the second flexible package further has a second flexible substrate, a second flexible semiconductor chip attached over the principal surface of the second flexible substrate, and second joint metals for connecting electrically the second flexible semiconductor chip and the second flexible substrate. The second flexible package further has a second sealing member sandwiched between the second flexible substrate and the second flexible semiconductor chip. On a principal surface of the second flexible substrate, a plurality of second metal wirings are disposed. The second metal wirings are connected electrically to the plurality of first metal wirings respectively. On a surface of the second flexible semiconductor chip, a plurality of second bonding pads are disposed. The second joint metals connects electrically the plurality of second bonding pads and the plurality of second metal wirings respectively.
According to the third feature of the present invention, a thickness necessary for a sheet of the semiconductor chip is reduced extremely so as to form the flexible semiconductor chip. And the respective constituent parts of the package such as the flexible substrate, etc. are also made thin. Therefore, by the stacked structure according to the third feature of the present invention, which is constructed by laminating a plurality of sheets of flexible semiconductor chips, the overall thickness of the MCM can be significantly reduced. Also, since the rigidity of respective semiconductor chips are made smaller, cracking, crazing, or damages, which might be caused by displacements due to differences in linear CTEs of the constituent parts, can be suppressed or avoided. As a result, the high packaging reliability as the product can be maintained.
A fourth feature of the present invention inheres in a method for manufacturing a module, which includes the steps of (a) reducing a thickness of a semiconductor chip into 10 xcexcm to 150 xcexcm; (b) delineating a plurality of packaging wirings on a principal surface of a packaging substrate; (c) delineating a plurality of metal wirings on a principal surface of a flexible substrate; (d) mounting the semiconductor chip over the principal surface of the flexible substrate; and (e) aligning the plurality of packaging wirings and the plurality of metal wirings, and then connecting electrically them mutually.
According to the fourth feature of the present invention, the module which has a small total thickness and has low rigidity and high packaging reliability can be manufactured easily, simply and at low cost so as to provide a high manufacturing yield.
Other and further objects and features of the present invention will become obvious upon an understanding of the illustrative embodiments about to be described in connection with the accompanying drawings or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employing of the invention in practice.